Thank you for your answers guys.
@Erel I made some tests and code modifications - it is the server capacity that is causing that error. I bought a cheap godaddy server for testing, so that is why this is happening. Despite claiming that the server can deal with up to 100 entry processes at the same moment, it freezes at around 20-30 or so. I will have to buy a new one, more powerful and faster.
@KMatle I do not use services for jobs. I dim the job, then initialize it, then poststring (and getrequest.timeout if needed) in an imageview click. I guess I should change it via service? About the question, that is a mistake. Since my php knowledge is not that good, I made more scripts with less code and that is why it is starting more than one job. I will have to unite the scripts to a maximum level. I got it, "less jobs - longer scripts" is better than "more jobs - shorter scripts". The server is one, and all I use is one database with several tables. For having 100k + users working at the same time I will need a dedicated server for sure. I expect about 100-200 users max at the same time. Any recommendations for a good and not that expensive server?